[PATCH v3 2/4] mm/balloon_compaction: remove balloon mapping and flag AS_BALLOON_MAP

From: Konstantin Khlebnikov
Date: Sat Sep 27 2014 - 15:16:38 EST

From: Konstantin Khlebnikov <k.khlebnikov@xxxxxxxxxxx>

Now ballooned pages are detected using PageBalloon(). Fake mapping
is no longer required. This patch links ballooned pages to balloon
device using field page->private instead of page->mapping. Also this
patch embeds balloon_dev_info directly into struct virtio_balloon.

Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@xxxxxxxxxxx>
Cc: Rafael Aquini <aquini@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/virtio/virtio_balloon.c | 60 +++++------------------
include/linux/balloon_compaction.h | 72 +++++++--------------------
include/linux/pagemap.h | 18 -------
mm/balloon_compaction.c | 95 ++----------------------------------
4 files changed, 39 insertions(+), 206 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index c3eb93fc..2bad7f9 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -59,7 +59,7 @@ struct virtio_balloon
* Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
* to num_pages above.
*/
- struct balloon_dev_info *vb_dev_info;
+ struct balloon_dev_info vb_dev_info;

/* Synchronize access/update to this struct virtio_balloon elements */
struct mutex balloon_lock;
@@ -127,7 +127,7 @@ static void set_page_pfns(u32 pfns[], struct page *page)

static void fill_balloon(struct virtio_balloon *vb, size_t num)
{
- struct balloon_dev_info *vb_dev_info = vb->vb_dev_info;
+ struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;

/* We can only do one array worth at a time. */
num = min(num, ARRAY_SIZE(vb->pfns));
@@ -171,7 +171,7 @@ static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
static void leak_balloon(struct virtio_balloon *vb, size_t num)
{
struct page *page;
- struct balloon_dev_info *vb_dev_info = vb->vb_dev_info;
+ struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;

/* We can only do one array worth at a time. */
num = min(num, ARRAY_SIZE(vb->pfns));
@@ -353,12 +353,11 @@ static int init_vqs(struct virtio_balloon *vb)
return 0;
}

-static const struct address_space_operations virtio_balloon_aops;
#ifdef CONFIG_BALLOON_COMPACTION
/*
* virtballoon_migratepage - perform the balloon page migration on behalf of
* a compation thread. (called under page lock)
- * @mapping: the page->mapping which will be assigned to the new migrated page.
+ * @vb_dev_info: the balloon device
* @newpage: page that will replace the isolated page after migration finishes.
* @page : the isolated (old) page that is about to be migrated to newpage.
* @mode : compaction mode -- not used for balloon page migration.
@@ -373,17 +372,13 @@ static const struct address_space_operations virtio_balloon_aops;
* This function preforms the balloon page migration task.
* Called through balloon_mapping->a_ops->migratepage
*/
-static int virtballoon_migratepage(struct address_space *mapping,
+static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
struct page *newpage, struct page *page, enum migrate_mode mode)
{
- struct balloon_dev_info *vb_dev_info = balloon_page_device(page);
- struct virtio_balloon *vb;
+ struct virtio_balloon *vb = container_of(vb_dev_info,
+ struct virtio_balloon, vb_dev_info);
unsigned long flags;

- BUG_ON(!vb_dev_info);
-
- vb = vb_dev_info->balloon_device;
-
/*
* In order to avoid lock contention while migrating pages concurrently
* to leak_balloon() or fill_balloon() we just give up the balloon_lock
@@ -399,7 +394,7 @@ static int virtballoon_migratepage(struct address_space *mapping,

/* balloon's page migration 1st step -- inflate "newpage" */
spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
- balloon_page_insert(newpage, mapping, &vb_dev_info->pages);
+ balloon_page_insert(vb_dev_info, newpage);
vb_dev_info->isolated_pages--;
spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
@@ -418,18 +413,11 @@ static int virtballoon_migratepage(struct address_space *mapping,

return MIGRATEPAGE_SUCCESS;
}
-
-/* define the balloon_mapping->a_ops callback to allow balloon page migration */
-static const struct address_space_operations virtio_balloon_aops = {
- .migratepage = virtballoon_migratepage,
-};
#endif /* CONFIG_BALLOON_COMPACTION */

static int virtballoon_probe(struct virtio_device *vdev)
{
struct virtio_balloon *vb;
- struct address_space *vb_mapping;
- struct balloon_dev_info *vb_devinfo;
int err;

vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
@@ -445,30 +433,14 @@ static int virtballoon_probe(struct virtio_device *vdev)
vb->vdev = vdev;
vb->need_stats_update = 0;

- vb_devinfo = balloon_devinfo_alloc(vb);
- if (IS_ERR(vb_devinfo)) {
- err = PTR_ERR(vb_devinfo);
- goto out_free_vb;
- }
-
- vb_mapping = balloon_mapping_alloc(vb_devinfo,
- (balloon_compaction_check()) ?
- &virtio_balloon_aops : NULL);
- if (IS_ERR(vb_mapping)) {
- /*
- * IS_ERR(vb_mapping) && PTR_ERR(vb_mapping) == -EOPNOTSUPP
- * This means !CONFIG_BALLOON_COMPACTION, otherwise we get off.
- */
- err = PTR_ERR(vb_mapping);
- if (err != -EOPNOTSUPP)
- goto out_free_vb_devinfo;
- }
-
- vb->vb_dev_info = vb_devinfo;
+ balloon_devinfo_init(&vb->vb_dev_info);
+#ifdef CONFIG_BALLOON_COMPACTION
+ vb->vb_dev_info.migratepage = virtballoon_migratepage;
+#endif

err = init_vqs(vb);
if (err)
- goto out_free_vb_mapping;
+ goto out_free_vb;

vb->thread = kthread_run(balloon, vb, "vballoon");
if (IS_ERR(vb->thread)) {
@@ -480,10 +452,6 @@ static int virtballoon_probe(struct virtio_device *vdev)

out_del_vqs:
vdev->config->del_vqs(vdev);
-out_free_vb_mapping:
- balloon_mapping_free(vb_mapping);
-out_free_vb_devinfo:
- balloon_devinfo_free(vb_devinfo);
out_free_vb:
kfree(vb);
out:
@@ -509,8 +477,6 @@ static void virtballoon_remove(struct virtio_device *vdev)

kthread_stop(vb->thread);
remove_common(vb);
- balloon_mapping_free(vb->vb_dev_info->mapping);
- balloon_devinfo_free(vb->vb_dev_info);
kfree(vb);
}

diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
index 38aa07d..bc3d298 100644
--- a/include/linux/balloon_compaction.h
+++ b/include/linux/balloon_compaction.h
@@ -57,21 +57,22 @@
* balloon driver as a page book-keeper for its registered balloon devices.
*/
struct balloon_dev_info {
- void *balloon_device; /* balloon device descriptor */
- struct address_space *mapping; /* balloon special page->mapping */
unsigned long isolated_pages; /* # of isolated pages for migration */
spinlock_t pages_lock; /* Protection to pages list */
struct list_head pages; /* Pages enqueued & handled to Host */
+ int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
+ struct page *page, enum migrate_mode mode);
};

extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
-extern struct balloon_dev_info *balloon_devinfo_alloc(
- void *balloon_dev_descriptor);

-static inline void balloon_devinfo_free(struct balloon_dev_info *b_dev_info)
+static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
{
- kfree(b_dev_info);
+ balloon->isolated_pages = 0;
+ spin_lock_init(&balloon->pages_lock);
+ INIT_LIST_HEAD(&balloon->pages);
+ balloon->migratepage = NULL;
}

#ifdef CONFIG_BALLOON_COMPACTION
@@ -79,14 +80,6 @@ extern bool balloon_page_isolate(struct page *page);
extern void balloon_page_putback(struct page *page);
extern int balloon_page_migrate(struct page *newpage,
struct page *page, enum migrate_mode mode);
-extern struct address_space
-*balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
- const struct address_space_operations *a_ops);
-
-static inline void balloon_mapping_free(struct address_space *balloon_mapping)
-{
- kfree(balloon_mapping);
-}

/*
* __is_movable_balloon_page - helper to perform @page PageBalloon tests
@@ -120,27 +113,25 @@ static inline bool isolated_balloon_page(struct page *page)

/*
* balloon_page_insert - insert a page into the balloon's page list and make
- * the page->mapping assignment accordingly.
+ * the page->private assignment accordingly.
+ * @balloon : pointer to balloon device
* @page : page to be assigned as a 'balloon page'
- * @mapping : allocated special 'balloon_mapping'
- * @head : balloon's device page list head
*
* Caller must ensure the page is locked and the spin_lock protecting balloon
* pages list is held before inserting a page into the balloon device.
*/
-static inline void balloon_page_insert(struct page *page,
- struct address_space *mapping,
- struct list_head *head)
+static inline void balloon_page_insert(struct balloon_dev_info *balloon,
+ struct page *page)
{
__SetPageBalloon(page);
SetPagePrivate(page);
- page->mapping = mapping;
- list_add(&page->lru, head);
+ set_page_private(page, (unsigned long)balloon);
+ list_add(&page->lru, &balloon->pages);
}

/*
* balloon_page_delete - delete a page from balloon's page list and clear
- * the page->mapping assignement accordingly.
+ * the page->private assignement accordingly.
* @page : page to be released from balloon's page list
*
* Caller must ensure the page is locked and the spin_lock protecting balloon
@@ -149,7 +140,7 @@ static inline void balloon_page_insert(struct page *page,
static inline void balloon_page_delete(struct page *page)
{
__ClearPageBalloon(page);
- page->mapping = NULL;
+ set_page_private(page, 0);
if (PagePrivate(page)) {
ClearPagePrivate(page);
list_del(&page->lru);
@@ -162,11 +153,7 @@ static inline void balloon_page_delete(struct page *page)
*/
static inline struct balloon_dev_info *balloon_page_device(struct page *page)
{
- struct address_space *mapping = page->mapping;
- if (likely(mapping))
- return mapping->private_data;
-
- return NULL;
+ return (struct balloon_dev_info *)page_private(page);
}

static inline gfp_t balloon_mapping_gfp_mask(void)
@@ -174,29 +161,12 @@ static inline gfp_t balloon_mapping_gfp_mask(void)
return GFP_HIGHUSER_MOVABLE;
}

-static inline bool balloon_compaction_check(void)
-{
- return true;
-}
-
#else /* !CONFIG_BALLOON_COMPACTION */

-static inline void *balloon_mapping_alloc(void *balloon_device,
- const struct address_space_operations *a_ops)
+static inline void balloon_page_insert(struct balloon_dev_info *balloon,
+ struct page *page)
{
- return ERR_PTR(-EOPNOTSUPP);
-}
-
-static inline void balloon_mapping_free(struct address_space *balloon_mapping)
-{
- return;
-}
-
-static inline void balloon_page_insert(struct page *page,
- struct address_space *mapping,
- struct list_head *head)
-{
- list_add(&page->lru, head);
+ list_add(&page->lru, &balloon->pages);
}

static inline void balloon_page_delete(struct page *page)
@@ -240,9 +210,5 @@ static inline gfp_t balloon_mapping_gfp_mask(void)
return GFP_HIGHUSER;
}

-static inline bool balloon_compaction_check(void)
-{
- return false;
-}
#endif /* CONFIG_BALLOON_COMPACTION */
#endif /* _LINUX_BALLOON_COMPACTION_H */
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 5ba1813..210b46b 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -24,8 +24,7 @@ enum mapping_flags {
AS_ENOSPC = __GFP_BITS_SHIFT + 1, /* ENOSPC on async write */
AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */
AS_UNEVICTABLE = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */
- AS_BALLOON_MAP = __GFP_BITS_SHIFT + 4, /* balloon page special map */
- AS_EXITING = __GFP_BITS_SHIFT + 5, /* final truncate in progress */
+ AS_EXITING = __GFP_BITS_SHIFT + 4, /* final truncate in progress */
};

static inline void mapping_set_error(struct address_space *mapping, int error)
@@ -55,21 +54,6 @@ static inline int mapping_unevictable(struct address_space *mapping)
return !!mapping;
}

-static inline void mapping_set_balloon(struct address_space *mapping)
-{
- set_bit(AS_BALLOON_MAP, &mapping->flags);
-}
-
-static inline void mapping_clear_balloon(struct address_space *mapping)
-{
- clear_bit(AS_BALLOON_MAP, &mapping->flags);
-}
-
-static inline int mapping_balloon(struct address_space *mapping)
-{
- return mapping && test_bit(AS_BALLOON_MAP, &mapping->flags);
-}
-
static inline void mapping_set_exiting(struct address_space *mapping)
{
set_bit(AS_EXITING, &mapping->flags);
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 52abeeb..3afdabd 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -11,32 +11,6 @@
#include <linux/balloon_compaction.h>

/*
- * balloon_devinfo_alloc - allocates a balloon device information descriptor.
- * @balloon_dev_descriptor: pointer to reference the balloon device which
- * this struct balloon_dev_info will be servicing.
- *
- * Driver must call it to properly allocate and initialize an instance of
- * struct balloon_dev_info which will be used to reference a balloon device
- * as well as to keep track of the balloon device page list.
- */
-struct balloon_dev_info *balloon_devinfo_alloc(void *balloon_dev_descriptor)
-{
- struct balloon_dev_info *b_dev_info;
- b_dev_info = kmalloc(sizeof(*b_dev_info), GFP_KERNEL);
- if (!b_dev_info)
- return ERR_PTR(-ENOMEM);
-
- b_dev_info->balloon_device = balloon_dev_descriptor;
- b_dev_info->mapping = NULL;
- b_dev_info->isolated_pages = 0;
- spin_lock_init(&b_dev_info->pages_lock);
- INIT_LIST_HEAD(&b_dev_info->pages);
-
- return b_dev_info;
-}
-EXPORT_SYMBOL_GPL(balloon_devinfo_alloc);
-
-/*
* balloon_page_enqueue - allocates a new page and inserts it into the balloon
* page list.
* @b_dev_info: balloon device decriptor where we will insert a new page to
@@ -61,7 +35,7 @@ struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
*/
BUG_ON(!trylock_page(page));
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
- balloon_page_insert(page, b_dev_info->mapping, &b_dev_info->pages);
+ balloon_page_insert(b_dev_info, page);
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
unlock_page(page);
return page;
@@ -127,60 +101,10 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
EXPORT_SYMBOL_GPL(balloon_page_dequeue);

#ifdef CONFIG_BALLOON_COMPACTION
-/*
- * balloon_mapping_alloc - allocates a special ->mapping for ballooned pages.
- * @b_dev_info: holds the balloon device information descriptor.
- * @a_ops: balloon_mapping address_space_operations descriptor.
- *
- * Driver must call it to properly allocate and initialize an instance of
- * struct address_space which will be used as the special page->mapping for
- * balloon device enlisted page instances.
- */
-struct address_space *balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
- const struct address_space_operations *a_ops)
-{
- struct address_space *mapping;
-
- mapping = kmalloc(sizeof(*mapping), GFP_KERNEL);
- if (!mapping)
- return ERR_PTR(-ENOMEM);
-
- /*
- * Give a clean 'zeroed' status to all elements of this special
- * balloon page->mapping struct address_space instance.
- */
- address_space_init_once(mapping);
-
- /*
- * Set mapping->flags appropriately, to allow balloon pages
- * ->mapping identification.
- */
- mapping_set_balloon(mapping);
- mapping_set_gfp_mask(mapping, balloon_mapping_gfp_mask());
-
- /* balloon's page->mapping->a_ops callback descriptor */
- mapping->a_ops = a_ops;
-
- /*
- * Establish a pointer reference back to the balloon device descriptor
- * this particular page->mapping will be servicing.
- * This is used by compaction / migration procedures to identify and
- * access the balloon device pageset while isolating / migrating pages.
- *
- * As some balloon drivers can register multiple balloon devices
- * for a single guest, this also helps compaction / migration to
- * properly deal with multiple balloon pagesets, when required.
- */
- mapping->private_data = b_dev_info;
- b_dev_info->mapping = mapping;
-
- return mapping;
-}
-EXPORT_SYMBOL_GPL(balloon_mapping_alloc);

static inline void __isolate_balloon_page(struct page *page)
{
- struct balloon_dev_info *b_dev_info = page->mapping->private_data;
+ struct balloon_dev_info *b_dev_info = balloon_page_device(page);
unsigned long flags;

spin_lock_irqsave(&b_dev_info->pages_lock, flags);
@@ -192,7 +116,7 @@ static inline void __isolate_balloon_page(struct page *page)

static inline void __putback_balloon_page(struct page *page)
{
- struct balloon_dev_info *b_dev_info = page->mapping->private_data;
+ struct balloon_dev_info *b_dev_info = balloon_page_device(page);
unsigned long flags;

spin_lock_irqsave(&b_dev_info->pages_lock, flags);
@@ -202,12 +126,6 @@ static inline void __putback_balloon_page(struct page *page)
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
}

-static inline int __migrate_balloon_page(struct address_space *mapping,
- struct page *newpage, struct page *page, enum migrate_mode mode)
-{
- return page->mapping->a_ops->migratepage(mapping, newpage, page, mode);
-}
-
/* __isolate_lru_page() counterpart for a ballooned page */
bool balloon_page_isolate(struct page *page)
{
@@ -274,7 +192,7 @@ void balloon_page_putback(struct page *page)
int balloon_page_migrate(struct page *newpage,
struct page *page, enum migrate_mode mode)
{
- struct address_space *mapping;
+ struct balloon_dev_info *balloon = balloon_page_device(page);
int rc = -EAGAIN;

/*
@@ -290,9 +208,8 @@ int balloon_page_migrate(struct page *newpage,
return rc;
}

- mapping = page->mapping;
- if (mapping)
- rc = __migrate_balloon_page(mapping, newpage, page, mode);
+ if (balloon && balloon->migratepage)
+ rc = balloon->migratepage(balloon, newpage, page, mode);

unlock_page(newpage);
return rc;

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